This invention relates to coating compositions for masking scuff marks on glass articles. More particularly, this invention relates to improved fast curing coating compositions for masking scuff marks on glass bottles.
Glass vessels which are used for beer, soft drinks, milk and the like in some countries are generally returnable and are recovered after use from the market and reused. During bottling processes, e.g., packaging, or transportation, such bottles undergo considerable abrasion damage, e.g., grazing, scratching, galling, scoring, and similar abrasive action (hereinafter referred to collectively as "scuffing") whereby scuff marks are left on the surfaces of the glass bottles. Scuffing phenomena is aggravated by mechanical grinding due to bottle-to-bottle pressure, mould lines, guide rails, and caustic etching and leaching. As a result, the appearance of the glass bottles is markedly impaired, and the commodity value of the resulting bottled beverages is lowered.
Efforts have been made to improve glass formulations and surface treatments for concealing scuff marks on bottle surfaces. Reference is made, for example, to U.S. Pat. Nos. 4,273,834 (Yokokura et al.); 4,656,221 (Kurita et al.); and 4,467,068 (Maruyama et al.).
U.S. Pat. No. 4,273,834 to Yokokura et al. (Yokokura) disclose a scuff-masking composition for glass vessels, wherein the composition comprises an organopolysiloxane terminated with a phenyl group, a methyl group, and an alkoxy group, and a curing catalyst, e.g., tetrabutyltitanate or dibutyltin dilaurate. The ratio of the phenyl, methyl, and alkoxy groups to one another is critical to the scuff-masking properties of the coating in Yokokura.
U.S. Pat. No. 4,656,221 to Kurita et al. (Kurita) discloses a composition for concealing graze marks on transparent glass bottles, the composition comprising a polydiorganosiloxane containing silicon-bonded organic groups selected from phenyl groups, aralkyl groups, and alkyl groups, a film-forming polyorganosiloxane containing a straight-chain diorganosiloxane portion and a cross-linking portion formed by the reaction of an amino or nitrogen group with an epoxy group and an oxygen atom, a cationic surfactant, and water.
U.S. Pat. No. 4,467,068 to Maruyama et al. (Maruyama) is directed to a composition for concealing grazes or scratches on glass surfaces, wherein the composition comprises an emulsion formed from a composition (A) which has as its principal ingredient a film-forming polyorganosiloxane and a composition (B) which has as its principal ingredient a liquid polydiorganosiloxane.
Another surface treatment presently used in Japan involves the use of a silicone coating containing organooxy-chainstopped organopolysilsequioxane, high levels of volatile diluent, e.g., greater than 75%, and low levels of curing catalyst. This silicone coating has several major drawbacks.
One drawback to the silicone coating described above is its inherent slow cure rate, i.e., approximately 2 to 4 days depending on the ambient conditions, which is the result of the coating's high content of volatile diluent and low content of curing catalyst, which inhibit cure rate. The slow cure rate in turn causes the coating to be tacky for a longer period of time. The increase in the tackiness period presents a problem because, in the United States, after the coating has been applied to the bottle surface, beer and soft drink bottles are packaged in clay-coated paper containers. The tackiness of the silicone coating on the bottle during the curing process causes the coating to pick up clay material from the paper container, resulting in blemishes on the surface of the coated bottle. Thus, the longer the coating is tacky, the more clay material is picked up and the more blemishes that result.
Another drawback to the silicon coating described above is its inability to completely cost "wet" bottle surfaces. In the united States, beer undergoes a pasteurization process wherein the bottle containing beer is immersed in a cold water bath and chilled. After completion of the pasteurization process, the chilled bottle is removed from the water bath and dried. However, water forms on the surface of the chilled bottle's surface as a result of condensation caused by the temperature difference between the chilled bottle and the ambient atmosphere, rendering the surface of the bottle wet.
The low solids silicone coating described above appears to coat the wet bottle completely but upon cure, the coating becomes uneven and forms blotches on the bottle surface, resulting in incomplete masking of scuff marks and an unattractive appearance.
It is an object of this invention, therefore, to provide a fast curing scuff-masking coating for glass articles.
It is a further object of this invention to provide a fast curing scuff-masking coating for glass articles, wherein the coating cures to form a uniform and non-blotchy coating on wet glass surfaces.
These objects are achieved in the present invention.